Distributed three-dimensional fiber Bragg grating refractometer for biochemical sensing.

We demonstrate a three-dimensional (3-D) distributed refractometer that measures refractive index in a small volume. The sensor is based on an evanescent-wave fiber Bragg grating that is interrogated by low-coherence spectral interferometry. The measurement can be performed on a short time scale without the need for a mechanical scan. The new sensor was used to simultaneously measure glucose concentration in several droplets along a single sensor and to interrogate the time-dependent evaporation process of a water droplet. The new measurement technique might enable novel 3-D distributed sensors to be developed and multiple discrete measurements to be made in a small volume.